Discovery and characterization of highly potent and selective allosteric USP7 inhibitors.

Given the importance of ubiquitin-specific protease 7 (USP7) in oncogenic pathways, identification of USP7 inhibitors has attracted considerable interest. Despite substantial efforts, however, the development of validated deubiquitinase (DUB) inhibitors that exhibit drug-like properties and a well-defined mechanism of action has proven particularly challenging. In this article, we describe the identification, optimization and detailed characterization of highly potent (IC50 < 10 nM), selective USP7 inhibitors together with their less active, enantiomeric counterparts. We also disclose, for the first time, co-crystal structures of a human DUB enzyme complexed with small-molecule inhibitors, which reveal a previously undisclosed allosteric binding site. Finally, we report the identification of cancer cell lines hypersensitive to USP7 inhibition (EC50 < 30 nM) and demonstrate equal or superior activity in these cell models compared to clinically relevant MDM2 antagonists. Overall, these findings demonstrate the tractability and druggability of DUBs, and provide important tools for additional target validation studies.

USP7 inhibitors suppress tumour neoangiogenesis and promote synergy with immune checkpoint inhibitors by downregulating fibroblast VEGF.

BACKGROUND: Understanding how to modulate the microenvironment of tumors that are resistant to immune checkpoint inhibitors represents a major challenge in oncology.Here we investigate the ability of USP7 inhibitors to reprogram the tumor microenvironment (TME) by inhibiting secretion of vascular endothelial growth factor (VEGF) from fibroblasts. METHODS: To understand the role played by USP7 in the TME, we systematically evaluated the effects of potent, selective USP7 inhibitors on co-cultures comprising components of the TME, using human primary cells. We also evaluated the effects of USP7 inhibition on tumor growth inhibition in syngeneic models when dosed in combination with immune checkpoint inhibitors (ICIs). RESULTS: Abrogation of VEGF secretion from fibroblasts in response to USP7 inhibition resulted in inhibition of tumor neoangiogenesis and increased tumor recruitment of CD8-positive T-lymphocytes, leading to significantly improved sensitivity to immune checkpoint inhibitors. In syngeneic models, treatment with USP7 inhibitors led to striking tumor responses resulting in significantly improved survival. CONCLUSIONS: USP7-mediated reprograming of the TME is not linked to its previously characterized role in modulating MDM2 but does require p53 and UHRF1 in addition to the well-characterized VEGF transcription factor, HIF-1α. This represents a function of USP7 that is unique to fibroblasts, and which is not observed in cancer cells or other components of the TME. Given the potential for USP7 inhibitors to transform "immune desert" tumors into "immune responsive" tumors, this paves the way for a novel therapeutic strategy combining USP7 inhibitors with immune checkpoint inhibitors (ICIs).

Identification and Structure-Guided Development of Pyrimidinone Based USP7 Inhibitors.

Ubiquitin specific protease 7 (USP7, HAUSP) has become an attractive target in drug discovery due to the role it plays in modulating Mdm2 levels and consequently p53. Increasing interest in USP7 is emerging due to its potential involvement in oncogenic pathways as well as possible roles in both metabolic and immune disorders in addition to viral infections. Potent, novel, and selective inhibitors of USP7 have been developed using both rational and structure-guided design enabled by high-resolution cocrystallography. Initial hits were identified via fragment-based screening, scaffold-hopping, and hybridization exercises. Two distinct subseries are described along with associated structure-activity relationship trends, as are initial efforts aimed at developing compounds suitable for in vivo experiments. Overall, these discoveries will enable further research into the wider biological role of USP7.